Metal Finishing Guide Book


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Fig. 8. Suction or dispersion piping system with strainer and siphon breaker. Drill a hole 2 in. below working solution level as a siphon breaker to prevent solution loss due to unforeseen damage to piping, pump, and so on. Chlorinated polyvinyl chloride with screwed connections offers maximum flexibility and ease in installation and may also be used on the return line by eliminating the strainer and replacing it with a longer length of pipe that is open along the full length. Bulk Carbon Method Granular or bulk carbon is poured loosely around standard depth-type cartridge filters or sleeves, is poured into specific chambers designed for carbon, or is pumped between the plates or disks of other surface media. Since no filter aid is used, fines breaking off from the piece of carbon will have to be stopped by the surface media. Therefore, an initial recirculation cycle without entering the plating tank or recirculation on the plating tank prior to plating is desirable. This method does not alter the solids-holding capacity of depth-type cartridges, as most of the carbon will stay on the outer surface layer; however, carbon removal is not easily accomplished. TIPS ON FILTER INSTALLATION Filtration equipment should be installed as close to the plating tank as possible in an area that affords access for servicing. Equipment that is not easy to service will not be attended to as frequently as required, and the benefits of filtration will not be maximized. The suction line should always have a larger diameter than the discharge to avoid starving the pump (e.g., 1 in. versus in. or 2 in. versus 1.5 in.) Where it is necessary to install the equipment more than 10 to 20 ft away, check the pump suction capabilities and increase the size of the suction piping (1.5 in. instead of 1 in., or 2 in. instead of 1.5 in.) to offset the pressure loss. Hoses made of rubber or plastic should be checked for compatibility with the different solutions. Strong, hot alkaline and certain acid solutions such as chromium are especially aggressive. The use of chlorinated polyvinyl chloride (CPVC), polypropylene, or other molded plastic piping for permanent installation is becoming more common. Some plastics are available with socket-type fittings, which are joined with solvents. Their chemical inertness and temperature capabilities are excellent. Iron piping, lined with either rubber or plastic, is ideal but usually limited to use on a larger tank capable of justifying the investment. It should be pointed out that whenever permanent piping can be used in and out of the tank a more reliable installation will exist, since there is no shifting to loosen fittings, and collapsing or sharp bending of hoses is eliminated. The suction should be located away from anode bags, to avoid their being drawn into the line and causing cavitation. Strainers on the suction are always advisable. It is also desirable to drill a small opening into the suction pipe below the normal solution operating level on permanent installations so that, should any damage occur to the system, the siphon action or suction of the pump will be broken when the level reaches the hold (Fig. 8). This provides added safety during unattended operation. Whenever automatic equipment is operated, 645

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